According to Heisenberg’s uncertainty principle, an eavesdropper cannot intercept any information unless they know the correct base. This makes it impossible for them to copy the qubits in transit, a limitation known as the no-cloning theorem. You can’t measure (or steal, or ‘borrow’) quantum information without disrupting it (i.e. breaking the superposition). If someone tries to do so, errors will inevitably creep into the communication.
